In process volumetric flow rate metrology, ultrasonic transit time meters are inter alia used for the measurement of the volumetric flow rate. They essentially comprise a measurement sensor that comprises a pipe piece having welded connector flanges, the ultrasonic transducers, also called ultrasonic probes and inserted into the pipe piece (middle piece) of the measurement sensor, as well as a signal processing unit for controlling the ultrasonic probes and for processing the signals output by the probes.
The measurement principle comprises a detection of a transit time difference of two ultrasonic signals that are irradiated or received in a direction that has a component in the direction of flow, on the one hand, and a component against the direction of flow, on the other hand. The signals have to be transmitted or received at a specific angle not equal to 90° with respect to the flow axis for this purpose. An ultrasonic flowmeter in accordance with this principle is known from EP 1 293 759 B1.
An exact determination of the pressure and of the temperature of the fluid is necessary for the calculation of the energy content from the measured value of the volumetric flow rate. Pressure and temperature sensors therefore have to be regularly calibrated. This is done nowadays by the external attachment of pipelines and blocking elements, which is complex and/or expensive and has the consequence of increased space requirements. US 2014/0109686 A1 shows such a design, for example. There is furthermore the risk that the external attachments are damaged during transport. The external attachments are also exposed to the environmental conditions and thus have to satisfy increased demands on leaktightness (IP protection). The electrical lines of the sensors are furthermore conducted to an evaluation unit in a manner accessible from the outside. Additional measures have to be provided for their protection from environmental influences.
A flowmeter for drinking water that comprises a pressure sensor, but does not have to be calibrated is known from DE 20 2015 006 553 U1.